Enhancing the Chiroptical Property of a 2D Lead Halide Perovskite via a Pseudo-Triple Cation Approach

Low-dimensional chiral perovskites have emerged as an interesting class of semiconductor materials with unique properties which hold promise for a range of applications including optoelectronics and spintronics. The insertion of chiral organic cations into the lattice of metal halide perovskites leads to the formation of 2D, 1D, and 0D perovskite structures with observed transfer of chirality to the inorganic framework. Despite the superior carrier mobility characteristic of chiral 2D perovskites relative to the 1D and 0D counterparts, they have so far been reported to possess the lowest degree of chirality – as assessed by the anisotropy factor of absorption (g_CD) and photoluminescence (g_PL) of circularly polarized light (CPL). This limits the utility and performance of chiral 2D perovskites in device applications such as in CPL photodetectors. Organic spacer cation mixing has proven a useful strategy to both modulate and enhance the chiroptical property of these 2D perovskites, but their corresponding g_CD values have yet to exceed the threshold of 10^-3 order of magnitude.<br/><br/>In this work, we rationalize a pseudo-triple cation approach which resulted in a record g_CD on the order of 10^-2 in a 2D metal halide perovskite, devoid of antisymmetric linear dichroism and linear birefringence (LDLB) contributions. By incorporating chiral enantiomers of 1-(1-Naphthyl)ethylamine (1NEA) and α-Methylbenzylamine (MBA) as spacer cations into the lattice of a lead bromide perovskite, we instigate the removal of mirror and inversion symmetries at both sub-lattice and local scales, induced by varied and asymmetric hydrogen bonding interactions, resulting in Rashba/Dresselhaus splitting of the electronic sub-bands - as revealed by Density Functional Theory (DFT) calculations.<br/><br/>Detailed characterization of the 2D mixed cation chiral perovskite revealed a strong preference for horizontal orientation via Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) measurements, large exciton confinement via absorption spectroscopy, and enhanced chirality with circular dichroism (CD) of ~2000 mDeg – yielding a g_CDvalue of ~0.03. Temperature-dependent circularly polarized transient absorption spectroscopy also unveiled picosecond spin depolarization kinetics of the perovskite system. The impact of temperature, composition, and solvent engineering on the resulting chiroptical properties of the perovskite system is also explored. These preliminary results showcase this material as a promising candidate for chiral optoelectronic and spintronic applications.<br/><br/>The unprecedented approach of employing pseudo-triple chiral cations provides a pathway to enhance the chiroptical properties of low-dimensional chiral perovskites and advances the ongoing efforts to elucidate the origin of these properties.